This work covers several areas of study of the structure of the murine Ia antigens, which are integral membrane glycoproteins encoded by genes in the I-region of the H-2 complex (MHC) of the mouse. The first objective is the elucidation of the structures of the oligosaccharides carried by Ia antigens. We will complete our studies of the carbohydrate moieties of the alpha and beta chains of the I-Ak antigen using radiochemical techniques. The second objective is the localization of the antigenic determinants of the I-Ak antigen. Monoclonal antibodies will be used to define the relationship between the antigenic structure and the primary structure of the I-Akantigen, since a large number of reagents are available for this antigen. If possible, this approach will be extended to the I-Ad antigen. The third objective is to carry out a detailed examination of the orientation of the Ia antigens in the lipid bilayer of the plasma membrane, including the development of markers for the extracellular, cytoplasmic, and membrane-integrating portions of the molecules. Within this general objective are experiments designed to search for potential interactions of Ia antigens with other membrane proteins or with cytoskeletal elements. A corollary of these experiments will be a search for potential interactions between Ia molecules, the foreign antigen, and the antigen-specific receptor of T cells. Experiments to accomplish the three objectives fall within the areas of immunochemistry and biochemistry. Ia antigens will be purified by affinity chromatography on monoclonal antibody columns, chains will be separated by SDS-PAGE or by ion exchange chromatography in acid-urea, and antigenic fragments will be monitored by indirect immunoprecipitation or by RIA. The primary approach to be employed in documenting the interaction of Ia antigens with other molecules will be the use of chemical cross-linkers. (CS)